Electroplating solution containing a diester of selenious acid



United States Patent 3,136,925 ELECTRGPLATHJG SGLUTEQN @ONTAiNiNG A DETER 0F SEiENiOUS ACID Hans Hofrnann, Neuss (Rhine), Germany (Gustav Klein Strasse 8, Stuttgart-Feuerbach, Germany), and Karl Wilhelm Sassenroth, Dusseldorf, Germany (Roonstrasse 65, Bielefeld, Germany) No Drawing. Filed Aug. 13, 1962, Star. No. 216,317 9 Claims. (Cl. 204-49) This invention relates to electrolytic deposition of bright metal coatings using electroplating baths to which brighteners are added. It is already known that additions of selenium compounds, preferably selenious acid or salts thereof, are active as brighteners in various electroplating baths.

Thus, it has already been proposed, a relatively long time ago, to use selenious acid and salts thereof as additives, together with an albumen condensation product, for silver baths for the production of bright silver coatings. Recently, it has also been proposed to use selenious acid in combination with various wetting agents in copper baths, as a brightener. Selenium dioxide is also known as an active brightener in nickel baths, and selenium compounds, namely selenium dithiocarbamate, and selenium in a form providing divalent negative ions have also already been proposed as additives for silver, gold and copper-plating baths.

We have found, unexpectedly, that selenium in the form of its very readily accessible selenious acid ester together with alcohols, phenols, thiophenols and thioalcohols, when used as an additive in the most diverse galvanic baths, gives a substantial improvement of the brightness, better throwing power, higher permissible current density and, in acid nickel baths, not only excellent brightness but also very considerable leveling eifect. From a large number of tests with the esters of selenious acid with a wide variety of alcohols, phenols, thioalcohols and thiophenols, we have found that apparently all the stable selenious acid esters, of which practically only the diesters exist, have the above-mentioned outstanding effects as brighteners in electroplating baths.

By selection of the compounds serving for the esteriz'ication and bearing OH or SH groups, by their constitution, and by further substitution, any desirable properties required for any specific electroplating bath can be obtained. Thus, by the introduction of further substituents, for example amino groups, sulpho-acid groups, it is possible to improve the water-solubility of the compounds in the various pH ranges, and with appropriate active groups to, improve the brightening eitect for the various metals.

Furthermore, by altering the size and structure of the molecule carrying the esterifiable groups, it is possible to obtain very good properties for the deposited metal coatings. The use of brighteners with high molecular weights according to the invention is advisable in electrolytic baths of the kind in which the metals deposited are not very sensitive to inhibitors, for example zinc and cadmium.

Apart from the selenious acid diesters, known brightening and leveling agents, hardening binders, pore-inhibiting agents, Wetting agents and so on may be added to the baths for further improvement and it special effects are required.

It is surprising that even very small quantities of selenious acid diest'ers give a high eiiect. Additions of about 0.00005 mol/litre to 0.2 mol/litre are used. In the case of baths for nickel deposition, it is advantageous also to add a small quantity of an acetylene amine.

The following examples illustrate the invention and the manner in which it is carried into effect:

Example 1 Very bright copper precipitates were deposited from a cyanidic bath of the following composition:

COpper as Na Cu(CN) g./l 50 NaCN (free cyanide) g./l 12 Seignette salt g./l 30 Dimethyl selenite m01/l 0.00005-01 Polyglycol ether g./l 0.5

at a bath temperature of 65 C., and with a moving cathode in the current density range from 0.2-3 a./dm.

Using a 30:1 current reversal cycle, the bright range is extended to a current density of 5 a./-dm.

Example 2 Uniform. very bright copper deposits were produced on a moving cathode from a cyanidic bath of the following composition:

Copper as Na Cu(CN) g./l 60 NaCN (free cyanide) g./l 15 Sodium citrate g./l 40 Bi-s-(phenosulfonic acid) selenite mol/l 000005-01 Polyglycol ether g./l 0.5 Acid amide sulpho-acids g./l 0.025

at 70 C., in a current density range from 0.2-4 a./drn. without current reversal. The cathode current yield is 9S-l00%.

Example 3 Mirror-bright completely cloud-free silver coatings were obtained from a silver bath of the following composition:

Silver in the form of KAg(CN) g./l 30 KCN (free cyanide) g./l K CO g./l 40 Bis-(2-naphthol-3,6-sulfonic acid) selenite "moi/1-- 000005-01 Turkey red oil g./l 1

and the brightness of these coatings is fully retained even with high coating thicknesses. The resultant silver deposits have a hardness of kgJmmP.

Example 4 A bath for the deposition of gold has the following composition:

Gold as KAu(CN) g./l 8 KCN (free cyanide) g./l 100 KgHPO g./1 Bis-(2-naphthol3,6-sultonic acid) 'selenite rnol/l 000005-01 Turkey red oil g./l 1

Very bright gold deposits were obtained at 20-50 C., in current density ranges of 0.1-3 a./dm.

Example 5 From a nickel bath of the following composition: MiSO -7H O g./l 280 NiCl 61-1 0 g./1 40 H 80 g./l 40 Benzoic acid sulphimide g./l 1 Bis-(o-aminophenol-sulph-onic acid) diseleni-te mol/l 000005-01 Lauryl sulphate g./l 0.5 Acetylene amine -g./1 0.015

mirror-bright ductile nickel deposit-s having a good leveling action were obtained at 60 C., in a current density range of 01-10 a./dm.

From the same bath, mirror bright deposits were also obtained at 20 C., without movement of the article in the current density range from 0.1-2 a./dm.

Example 6 7 From a nickel bath of the following composition:

NiSO '-7H O g./l 280 NiCl -6H O g./l 40 H3803 g./l Naphthalene trisulfonic acid g./l 10 Diethyl selenite mol/l 0.000050.l Lauryl sulphate g./l 0.5 Acetylene amine g./l 0.015

nickel deposits were obtained as in Example 5.

' Example 7 Very bright zinc deposits were obtained from a cyanidic zinc bath of the following composition:

Zinc as Na Zn(CN) g./l 30 NaCN (total cyanide) g./l 50 NaOH g./l 90 Diglycerine selenite ml/l (100005-01 at 20 C., in current density ranges of from 0.1 6 a./dm. Example 8 Very bright deposits were obtained from a cyanidic cadmium bath of the following composition:

Cadmium as Na Cd(CN) g./l 25 NaCN (total cyanide) g./l 100 NiSO -7H O g./l. 1 Di-polyglycol (M.W. 600) selenite mol/l 0.000050.1 Polyglycol ether g./l 1

at 20 0., in current density ranges of from 0.5-10 a./ dm. and with cathode movement.

7 We claim:

1. An aqueous bath for the electrolytic deposition of bright metal coatings, including an ionizable compound of the metal to be deposited, and as a brightener, an effective amount of a stable diester of selenious acid.

2. An aqueous bath for the electrolytic deposition of bright nickel including an ionizable nickel compound and, as a brightener, an effective amount of a stable diester of selenious acid. I

3. An aqueous bath for the electrolytic deposition of bright nickel including an ionizable nickel compound and,

4 as a brightener, a stable diester of selenious acid in a concentration between 0.00005 and 0.2 mol per liter.

4. An electroplating solution comprising, in aqueous solution, an ionizable compound of a metal to be deposited electrolytically, said solution containing, as a brightener, a stable diester of selenious acidin a concentration between 0.00005 and 0.2 mol per liter.

5. An aqueous electroplating solution comprising a cyanide salt of a metal to be deposited electrolytically, said solution containing, as a brightener, an effective amount of a stable diester of selenious acid.

6. A method of depositing a bright metal coating which comprises electrolyzing an equeous solution of an ionizable compound of said metal, said solution including an effective amount of a stable diester of selenious acid as a biightener.

7. An electroplating bath comprising an aqueous solution of a source of a metal to be electrodeposited, said source being selected from the group consisting of the complex cyanides of copper, silver, gold, zinc, and cadmium, and the sulfate and chloride of nickel, said solution containing, as a brightener, an effective amount of a stable diester of selenious acid with a compound selected from the group consisting of the lower alkanols, phenosulfonic acid, 2-naphthol-3,6-sulfonic acid, o-aminophcnol-sulfonic acid, glycerine, and polyglycol.

8. A method of electrodepositing bright nickel which comprises electrolyzing an aqueous medium containing nickel sulfate, as a source of nickel ions and, as a brightener, an effective amount of a stable diester of selenious acid with a compound selected from the group consisting of the lower alkanols, phenol-sulfonic acid, 2- naphthol-3 ,6-sulfonic acid, o-a-minophenolsulfonic acid, glycerine, and polyglycol.

9. A method as set forth in claim 8, wherein the concentration of said diester in said aqueous medium is bc-- tween 0.00005 and 0.2 mol per litter.

References Cited by the Examiner UNITED STATES PATENTS 2,701,234 2/55 Wernlund 204-52.l 2,770,587 11/56 Ostro-w 20452.1 2,777,810 1/57 Ostrow 20446 JOHN H. MACK, Primary Examiner. MURRAY TILLMAN, Examiner. 

1. AN AQUEOUS BATH FOR THE ELECTROLYTIC DEPOSITION OF BRIGHT METAL COATING, INCLUDING AN IONIZABLE COMPOUND OF THE METAL TO BE DEPOSITED, AND AS A BRIGHTNER, AN EFFECTICE AMOUNT OF A STABLE DIESTER OF SELENIOUS ACID. 